I have set my copy of Groupy to those colours and as expected things look as you request. The issue seems to be for some reason the inactive tabs colours are not painting which is why you are seeing white text on a light background.
An active tab is the active tab in a group, so active tab colour is the selected tab in a group that has focus. The non focused version of this colour is used when the group is not the foreground window/group.
Likewise the inactive tab colours are used for the other tabs which are not the selected tabs in the group.
The text colour is automatically picked depending on if it needs to be black or white based on the colours. For some reason on your computer the colour being picked is correct for the colour you have picked for inactive tabs, but it is then not painting that background colour.
If you pick a different system wide colour in Windows settings for your accent / titlebar colour, does it have any impact?